Can off-diagonal density matrix terms be zero while diagonal terms are nonzero?

[harish.ravi]

In a density matrix, can some coherances (off diagonal terms) be zero while the diagonal terms(populations) aren't? I am confused because rhoij=Ci*Cj'. How can coherance be zero if Ci and Cj aren't?

 

[alxm]

Yse, coherences can be zero. If you're at equilibrium, they're all zero.

 

[Avodyne]

Your density matrix applies to a "pure state" only. Look up "pure states" and "mixed states".